1. Field of the Invention
The present invention relates to a semiconductor memory device. More particularly, the invention relates to a semiconductor memory which includes a memory cell having a charge accumulating layer and a control gate.
2. Description of the Related Art
Conventionally, an electrically erasable and programmable ROM (EEPROM) has been well known as a nonvolatile semiconductor memory which is rewritable electrically. A method for controlling the EEPROM using a microcomputer has been disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2002-269065.
In case of controlling the EEPROM by a microcomputer, a flash memory circuit is controlled using a signal with small bits which is supplied from a processor and which is transmitted by address line, data line and write control line. Therefore, this has an advantage that the quantity of the signal wires can be reduced. Further, change and correction of the content of automatic control by the microcomputer are carried out by changing and correcting software for operating the processor. Thus, there is such a merit that correction of a circuit itself is not required, thereby suppressing cost of manufacturing process.
However, as demerits of EEPROM control by a microcomputer, a time-lag is generated from an input of automatic operation start command up to startup of the microcomputer and the quantity of signal wires which can be controlled at a time is limited, thereby retarding the processing.